This invention relates to cleaning metal surfaces, both painted and unpainted, more particularly when the metal surfaces are adjacent to elements of plastic, especially polycarbonate plastic, which is susceptible to stress cracking when repeatedly contacted with many conventional metal cleaning compositions. This invention also relates to cleaning compositions that are useful in such cleaning processes, are not overly acidic or alkaline, and are not susceptible to developing undesirable odors from micro-organisms that readily come into contact with the compositions during normal storage or use.
A very wide variety of cleaning compositions are known in the art. Few if any of these compositions, however, are known to be capable of fulfilling all the desiderata noted above, particularly for railroad cars that are powered by electricity. Such cars, like other railroad cars, come into contact with a wide variety of atmospheric pollutants and air-borne soils that often lead to rapid deterioration in the aesthetic appearance of the exteriors of the cars. Ordinary rail cars that do not supply their own motive power can be readily cleaned by a variety of cleaners, usually most readily by fairly highly alkaline cleaners. However, rail cars that are directly powered by electricity, a type especially frequently used in mass transit operations, generally have housings of polycarbonate plastic on their exterior surfaces to protect electrical contacts that supply power to move the cars from a "third rail", overhead power line, or the like. This plastic readily develops stress cracks when contacted repeatedly by many alkaline solutions, including some of the most generally effective aqueous metal cleaning compositions. Such large vehicles can most conveniently be cleaned by sprayers, but it is a practical impossibility in many cases to protect any plastic parts of the exterior surface from contact with a sprayed cleaner composition, and frequent replacements of the plastic insulating housings are economically unacceptable.
Major objects of the present invention are to provide compositions and/or processes that (i) effectively clean painted and unpainted metal surfaces, (ii) do not damage any plastic materials, particularly polycarbonate plastic insulating housings, that are adjacent to the metal surfaces to be cleaned, (iii) are not susceptible to becoming malodorous as a result of infestation from commonly ambient micro-organisms, and (iv) do not have a pH lower than about 3 or higher than about 9, so as to minimize the likelihood of personal injuries to workers using the cleaners. A subsidiary object is to brighten unpainted aluminum surfaces, particularly those of Type 6061 T6 aluminum, that are cleaned using the compositions. Other objects will be apparent from the description below.
Except in the claims and the specific examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, unless expressly stated to the contrary: percent, "parts of", and ratio values are by weight; the term "polymer" includes "oligomer", "copolymer", "terpolymer", and the like; the first definition or description of the meaning of a word, phrase, acronym, abbreviation or the like applies to all subsequent uses of the same word, phrase, acronym, abbreviation or the like and applies, mutatis mutandis, to normal grammatical variations thereof; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; chemical descriptions of materials apply to the materials at the time of addition to any combination specified in the description or of generation within the composition by chemical reactions specified in the description between a newly added material and a distinct material already present, and do not necessarily preclude chemical changes to the materials as a result of reaction in the combination; in addition, specification of materials in ionic form means that the materials are supplied to prepare the compositions containing them in the form of soluble salts containing the ions specified and implies the presence in any composition specified to contain ionic materials of sufficient counterions to produce electrical neutrality for the composition as a whole; and any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to the objects of the invention.